Field of the Invention
The invention relates to a method for determining a fill level of a medium using the radar principle. Furthermore, the invention relates to a device for determining a fill level of a medium using the radar principle.
Description of Related Art
In industrial measuring technology, radar fill level measuring devices are used to determine fill levels of media such as liquids, bulk materials or also slurries within containers such as tanks or silos or also in open spaces. Thereby, the container can be at least partially closed or at least partially open and consist at least partially of metal, plastic, ceramic or other materials or material combinations. The transit time method used in measurement is based on the transit path of an electromagnetic signal being equal to the product of transit time and propagation velocity.
Electromagnetic signals—in particular microwave signals—are transmitted in the direction of the surface of the medium and received after a reflection as so-called echo signal. The antenna, which is used as transmitting device for transmitting the signal, is often also the receiving device. Often, a digitalized envelope is determined for evaluating the received signal, which represents the amplitudes of the echo signals as a function of distance “antenna—surface of the medium”. The fill level results from the difference between the known distance of the antenna to the floor of the container and the distance of the surface of the medium to the antenna determined in the measurement.
Thereby, the microwave signals are either freely emitted or are guided along a cable or rod.
How the antenna or the transmitting device is oriented relative to the surface of the medium is relevant for determining the fill level. In most cases, the transmitting or transmitting/receiving device is mounted vertically over the medium. The electromagnetic signals are thus, generally, transmitted perpendicular to the surface of the medium.
However, it is possible that the antenna has to be mounted at an angle due to particular mounting situations or, for example, the presence of fixtures as disturbing elements in the container.
The German Patent Application DE 10 2004 041 857 A1 and International Patent Application Publication WO 2012/089438 A1 which corresponds to U.S. Patent Application Publication 2013/269414 A1 describe the use of slope sensors for such cases, in order to obtain the angle at which the antenna is sloped. The distance between the antenna and the surface of the medium are determined using trigonometric correlations.